1. Field of the Invention
The invention relates to a drive transmission for a pull or forwarding sucker, in particular, for a device for correcting misaligned sheets, the pull sucker drive transmission being located in a suction head of a sheet feeder for translatorily driving a sucker-carrying support movable in a guide provided on a suction-head housing, the sucker-carrying support being connected articulatingly to at least one couple element or coupler swivelable about an axis extending transversely to the translatory motion of the sucker-carrying support, the couple element being movable by a drive cam. The drive transmission for the pull or forwarding sucker is particularly suited for providing the misalignment-correction device in the suction head of the sheet feeder of a sheet-fed printing press.
A drive transmission for a pull or forwarding sucker having the foregoing general features has become known heretofore from the German Patent 11 77 652 wherein two spaced-apart pull or forwarding suckers are provided at pipe branches on a sucker-carrying support formed of a pipe disposed transversely to a translatory sucker movement. The sucker-carrying support is connected, by substantially vertically extending tubular connecting members, to a shaft fixedly mounted on the press. The drive is effected by a drive cam which acts against a roller lever on the shaft, a lever attached to the sucker-carrying support engaging in a stationary coulisse or connecting-link guide in order to produce a forwarding or conveying stroke of the respective suckers. For a misalignment correction, such as a correction of a skewed sheet, one of the two suckers may be slightly rotated about the transverse axis thereof. For this purpose, the respective sucker is connected to a pull rod by a lever, an articulated connection between the pull rod and the sucker-carrying support being displaceable by adjusting elements. The adjusting elements can be actuated only when the printing press is at a standstill. When more than two pull or forwarding suckers are used, a sheet misalignment correction inevitably causes a distortion of the paper sheet.
German Patent 21 32 438 discloses a linear guide for forwarding or pull suckers. In order to absorb torques occurring in the guides, additional rollers are provided and v-shaped guide rails are used, respectively. Assembling or mounting the rollers and v-shaped guide rails requires a considerable outlay of technical effort, if a play-free setting is to be achieved. This conventional linear guide uses needle bearings and, at high operating speeds, the needles do not reliably roll off in the guides due to high resulting accelerations.
This leads to increased wear and tear. According to the German Published and Prosecuted Patent Application (DE-AS) 22 25 001, the misaligned-sheet correction device constructed on this conventional linear guide has a swivel or hinge joint in order to be able to rotate the sucker-carrying support, the axis of the swivel being perpendicular to the sheet surface. A relatively complex mounting support is required to avoid tilting effects at the sucker-carrying support. This is in conjunction with an increase in the translatorily moved masses, due to which especially the joints are greatly stressed.
A misaligned-sheet correction device also suitable for translatorily moved sucker-carrying supports has become known heretofore from the German Utility Model or Petty Patent (DE-GM) 72 03 336, the relatively complex construction of the misaligned-sheet correction device having dynamically similar undesirable properties.
In a device according to the aforementioned German Patent 11 77 652, suckers are located on a coupler or connecting rod which is guided by swinging or rocking levers and a cam segment. Thus, suckers provided at arbitrary locations may not execute a purely translatory transport or conveying movement. The misaligned-sheet correction may be performed only by using two suckers, because it is effected by pivoting a sucker about a horizontal axis extending transversely to the paper travel direction.
A basically comparable arrangement for three suckers is disclosed in the German Patent 21 63 083. The three suckers are arranged symmetrically to the center of the sheet in order to ensure that the sheet is only slightly distorted.
The German Patent 17 86 029 describes a drive transmission for a forwarding or pull sucker provided in a suction head of a sheet feeder wherein a sucker-carrying support carrying an arbitrary number of suckers is articulatedly connected to a swinging half-axle and, by a control cam, aligns the sheet with the leading edge thereof during the feed or stroke, and indeed so that the pipe carrying the suckers is mounted so as to be swivelable in the middle thereof about the vertical axis thereof and is connected to a lever having a free end which slides in a guide angularly adjustable with respect to the sheet-transport or travel direction.